Expression profiling of flowering time pathway in the L-ascorbate peroxidase 9 (APX9) near-isogenic line derived from an interspecific cross between Korean Japonica rice (Oryza sativa L.) and Oryza rufipogon.

BACKGROUND

Flowering time (referred to as heading date in rice) is a characteristic controlled by quantitative trait loci (QTLs). Heading date is an important agronomic trait that determines yield in rice and is precisely regulated by various exogenous and endogenous factors.

OBJECTIVE

To investigate the role of the ascorbate peroxidase 9 (APX9) gene in the flowering mechanism, we examined the expression levels of flowering time regulators under long-day conditions (14 h light/10 hours dark) and natural long-day conditions.

METHODS

A BCF near-isogenic line (NIL), derived from an interspecific cross between the Korean elite japonica cultivar (cv. Hwaseong, Oryza sativa L.) and Oryza rufipogon (IRGC 105491), was used in this study to identify and characterize candidate genes associated with heading traits. The NIL contains a small O. rufipogon chromosome segment harboring the APX9 gene. In addition, overexpression and T-DNA insertion knockout transgenic lines were used to examine the function of APX9 gene.

RESULTS

The NIL exhibited delayed flowering under both controlled and natural long-day conditions compared to Hwaseong. Real-time PCR analysis indicated that APX9 influences the upstream pathway of flowering time regulation. Over-expression lines showed delayed flowering relative to Hwaseong, whereas T-DNA mutants flowered earlier than the control cultivar, Dongjin. These findings support a role for APX9 in modulating flowering time in rice.

CONCLUSION

The APX9 is known for its antioxidant activity and its response to various abiotic stresses. The APX9 may play a role in the upstream regulation of the flowering pathway. These findings will be valuable in understanding the effect of APX9 during flowering stages. It would also be interesting to explore the relationship between hydrogen peroxide (HO levels and the APX9 gene in signaling events related to heading.